1. Field of the Invention
This invention relates generally to an automatic white balance adjustment method and apparatus. More particularly, this invention relates to an automatic white balance adjustment method and apparatus for adjusting a white balance according to a type of a light source.
2. Description of Related Art
In a conventional white balance adjustment method, a differential signal (R−B) is calculated between a mean value of R signals and a mean value of B signals among red (R), green (G) and blue (B) signals on the whole image. A white balance is adjusted by adjusting gains of the R signals and the B signals so that the differential signal (R−B) can approach 0. In this method, however, the white balance is not properly adjusted if the color temperature of a subject is distributed unevenly or if major parts of the image have a single color.
In another conventional white balance adjustment method, the range for adjusting the gains of R and B signals is limited according to a luminance level of the subject so that the white balance can be adjusted correctly (Japanese Patent Provisional Publication No. 5-64219). For a scene in which the differential signal (R−B) cannot approach 0, however, this conventional method only just reduces the incorrect adjustment, and the white balance cannot be suitably adjusted by this conventional method that adjusts the white balance so that the differential signal (R−B) can approach 0.